The World Wide Web can be considered as a large distributed information system that provides access to shared data objects. As one of the most popular applications currently running on the Internet, the World Wide Web is of an exponential growth in size, which results in network congestion and server overloading. Web caching has been recognized as one of the effective schemes to alleviate the service bottleneck and reduce the network traffic, thereby minimize the user access latency. In this paper, we first describe the elements of a Web caching system and its desirable properties. Then, we survey the state-of-art techniques which have been used in Web caching systems. Finally, we discuss the research frontier in Web caching.

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A survey of web caching schemes for the Internet

Resource requests made by clients of origin servers in a network are intercepted by reflector mechanisms and selectively reflected to other servers called repeaters. The reflectors select a best repeater from a set of possible repeaters and redirect the client to the selected best repeater. The client then makes the request of the selected best repeater. The resource is possibly rewritten to replace at least some of the resource identifiers contained therein with modified resource identifiers designating the repeater instead of the origin server.

Optimized network resource location

Most researches in ad hoc networks focus on routing and not much work has been done on data access. A common technique used to improve the performance of data access is caching. Cooperative caching, which allows the sharing and coordination of cached data among multiple nodes, can further explore the potential of the caching techniques. Due to mobility and resource constraints of ad hoc networks, cooperative caching techniques designed for wired networks may not be applicable to ad hoc networks. In this paper, we design and evaluate cooperative caching techniques to efficiently support data access in ad hoc networks. We first propose two schemes: CacheData, which caches the data, and CachePath, which caches the data path. After analyzing the performance of those two schemes, we propose a hybrid approach (HybridCache), which can further improve the performance by taking advantage of CacheData and CachePath while avoiding their weaknesses. Cache replacement policies are also studied to further improve the performance. Simulation results show that the proposed schemes can significantly reduce the query delay and message complexity when compared to other caching schemes.

Supporting cooperative caching in ad hoc networks

Academic and corporate communities have been dedicating considerable effort to World Wide Web caching. When correctly deployed, Web caching systems can lead to significant bandwidth savings, server load balancing, perceived network latency reduction, and higher content availability. We survey the state of the art in caching designs, presenting a taxonomy of architectures and describing a variety of specific trends and techniques.

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World Wide Web caching: trends and techniques

We present a new class of low-bandwidth denial of service attacks that exploit algorithmic deficiencies in many common applications' data structures. Frequently used data structures have "average-case" expected running time that's far more efficient than the worst case. For example, both binary trees and hash tables can degenerate to linked lists with carefully chosen input. We show how an attacker can effectively compute such input, and we demonstrate attacks against the hash table implementations in two versions of Perl, the Squid web proxy, and the Bro intrusion detection system. Using bandwidth less than a typical dialup modem, we can bring a dedicated Bro server to its knees; after six minutes of carefully chosen packets, our Bro server was dropping as much as 71% of its traffic and consuming all of its CPU. We show how modern universal hashing techniques can yield performance comparable to commonplace hash functions while being provably secure against these attacks.

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Denial of service via algorithmic complexity attacks

We describe the structure and functionality of the Internet cache protocol (ICP) and its implementation in the Squid web caching software. ICP is a lightweight message format used for communication among Web caches. Caches exchange ICP queries and replies to gather information to use in selecting the most appropriate location from which to retrieve an object. We present background on the history of ICP, and discuss issues in ICP deployment, efficiency, security, and interaction with other aspects of Web traffic behavior. We catalog successes, failures, and lessons learned from using ICP to deploy a global Web cache hierarchy.

ICP and the Squid web cache

This document describes the application of ICPv2 (Internet Cache Protocol version 2, RFC2186) to Web caching. ICPv2 is a lightweight message format used for communication among Web caches. Several independent caching implementations now use ICP[3,5], making it important to codify the existing practical uses of ICP for those trying to implement, deploy, and extend its use.

D. Wessels

Papers

ICP and the Squid web cache

Application of Internet Cache Protocol (ICP), version 2